review: address feedback — update navigation tree on cut/paste

When nodes with subgraphs are cut and pasted to a different graph,
reparent their tree entries so the sidebar tree and breadcrumbs
reflect the new hierarchy.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

e2e/breadcrumb.spec.ts

@@ -102,5 +102,92 @@ test.describe('Breadcrumb navigation', () => {
     await expect(breadcrumbLinks(page)).toHaveCount(2, { timeout: 3000 });
     await expect(page.locator('.ant-breadcrumb')).toContainText('End');
     await expect(page.locator('.ant-breadcrumb')).not.toContainText('Start');
-  });  
+  });
+});
+
+// Regression tests for issue #2: stale closure caused breadcrumbs to disappear on back-navigation.
+//
+// The bug: createPathSegment's onClick closed over `graphsPath` from the render in which
+// the segment was created. After further navigation the closure was stale, so findIndex
+// returned -1 and splice(0) wiped the entire breadcrumb array.
+//
+// The fix: use the functional updater form of setGraphsPath so findIndex always runs
+// against the *current* state rather than a captured snapshot.
+test.describe('Stale-closure regression (issue #2)', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+    await waitForGraph(page);
+  });
+
+  test('root breadcrumb remains functional after navigating three levels deep', async ({ page }) => {
+    // Navigate 3 levels deep — each additional level re-renders breadcrumbs with new
+    // closures; before the fix, clicking the root would hit a stale closure from level 1
+    // and wipe everything.
+    await openSubgraph(page, 'Start');  // level 1
+    await openSubgraph(page, 'Start');  // level 2
+    await openSubgraph(page, 'Start');  // level 3
+    await expect(breadcrumbLinks(page)).toHaveCount(4);
+
+    // Click the root ("Main") breadcrumb
+    await breadcrumbLinks(page).first().click();
+
+    // Breadcrumbs must NOT disappear — exactly one "Main" segment remains
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Main');
+    await waitForGraph(page);
+    // The root graph is rendered correctly
+    await expect(nodeByLabel(page, 'Start')).toBeVisible();
+    await expect(nodeByLabel(page, 'End')).toBeVisible();
+  });
+
+  test('level-1 breadcrumb remains functional when clicked from level 3', async ({ page }) => {
+    // This is the core regression scenario: a breadcrumb segment created at level 1
+    // must still resolve correctly after two more navigations have updated the path state.
+    await openSubgraph(page, 'Start');  // level 1
+    await openSubgraph(page, 'Start');  // level 2
+    await openSubgraph(page, 'Start');  // level 3
+    await expect(breadcrumbLinks(page)).toHaveCount(4);
+
+    // Click the level-1 breadcrumb (second item)
+    await breadcrumbLinks(page).nth(1).click();
+
+    // Should trim to exactly 2 items — NOT clear everything
+    await expect(breadcrumbLinks(page)).toHaveCount(2, { timeout: 3000 });
+    await waitForGraph(page);
+    // The graph at level 1 is shown
+    await expect(nodeByLabel(page, 'Start')).toBeVisible();
+  });
+
+  test('successive back-clicks each trim exactly one breadcrumb level', async ({ page }) => {
+    await openSubgraph(page, 'Start');  // level 1
+    await openSubgraph(page, 'Start');  // level 2
+    await openSubgraph(page, 'Start');  // level 3
+    await expect(breadcrumbLinks(page)).toHaveCount(4);
+
+    // Click level-2 breadcrumb
+    await breadcrumbLinks(page).nth(2).click();
+    await expect(breadcrumbLinks(page)).toHaveCount(3, { timeout: 3000 });
+
+    // Then click level-1 breadcrumb
+    await breadcrumbLinks(page).nth(1).click();
+    await expect(breadcrumbLinks(page)).toHaveCount(2, { timeout: 3000 });
+
+    // Then click root breadcrumb
+    await breadcrumbLinks(page).first().click();
+    await expect(breadcrumbLinks(page)).toHaveCount(1, { timeout: 3000 });
+    await expect(page.locator('.ant-breadcrumb')).toContainText('Main');
+  });
+
+  test('clicking the active (last) breadcrumb does not alter the path', async ({ page }) => {
+    // Clicking the segment you are already on should be a no-op — it must not clear
+    // breadcrumbs by accidentally slicing at index -1.
+    await openSubgraph(page, 'Start');  // level 1
+    await openSubgraph(page, 'Start');  // level 2
+    await expect(breadcrumbLinks(page)).toHaveCount(3);
+
+    // The last breadcrumb link is the currently active level
+    await breadcrumbLinks(page).last().click();
+
+    await expect(breadcrumbLinks(page)).toHaveCount(3, { timeout: 3000 });
+  });
 });